V-scoring is a viable process selection for both low and high volume production
because it allows for maximum material utilization. V-scoring is also a preferred
process for prototypes with rectangular geometries having the benefit of no
tooling costs. Holes can be drilled or punched prior to scoring.Typical tolerance
for part size, hole position to part edge, and circuit to edge is +/- 0.25mm (0.010").
V-scoring is a great alternative for arrays. Circuit to edge spacing can be
reduced over a typical blanked part (see Section 1.4 on page 4 of this document).
Hole Piercing / Perimeter Blanking
Hole piercing and perimeter blanking are some of the most cost effective
processes for moderate to high volume applications. Blank tooling can
accommodate complex part geometries and can be held to a very tight
tolerance. In addition to blanking the part perimeter, piercing patterns of
internal holes can be produced with the most accuracy and the greatest
degree of repeatability. However,T-Clad that is to be blanked in production
should be considered as early in the design process as possible. Part
design is critical to ensure blanking feasibility as there are specific
guidelines to be considered. Each design should be evaluated to the
recommendations defined in this document prior to beginning the tool
Milling / Drilling
Milling/drilling processes are typically used for prototype or low volume production with complex geometries.These processes are typically not cost effective for moderate to high volume applications.
Circuit to Edge
When planning to blank a part perimeter, the distance between the circuit pattern and the part edge is critical.To allow for sufficient relief for the circuitry (See Figure 4), the standard minimum distance from circuit to part edge is one material thickness plus 0.5mm (0.020"). If the circuit foil is 2oz or higher, the face of the perimeter punch must be designed to allow for uniform support around the part perimeter.
Active circuitry that needs to be isolated from the base plate should be placed a minimum of one material thickness plus 0.5mm (0.020") from the edge of the hole. If the circuit is a ground pattern, or same potential as the base plate, then the circuitry may go closer. Standard practice is to always leave a 1.3mm (0.051") relief around a pierced hole. Note: The minimum diameter we can pierce is equivalent to one material thickness. Higher voltages may require greater clearances.
Figure 4: Punch to Die Clearance
Radii on Corners
Punching requires that all inside and outside corners be designed with a minimum radius. It is recommended that one material thickness minimum radius be on all corners. When desired, it is possible to go down to one half material thickness
Part design, as well as the manufacturing process, affects flatness of an Insulated Metal Substrate (IMS®) board. There is also an effect from the differential coefficient of thermal expansion (CTE) between the circuit and the base layer.That effect is determined by the base plate material selection and ratio of copper foil to base plate thickness.
For IMS®, panel or part, there is always the potential for some bow caused by the difference in CTE between the circuit layer and the base plate. Flatness can be further optimized by using copper base metal instead of aluminum and with proper overall design. Generally, if the thickness of the copper layer is less than 10% of the substrate thickness, the aluminum will be mechanically dominant. Constructions with more circuit copper than 10% of the substrate thickness can exhibit a bow. Copper foil thicknesses less than 10% of the base plate thickness can be controlled well within IPC specifications. Flatness can be further optimized with proper tool design.